1. Field of the Invention
The present invention relates to a liquid injector for injecting a liquid into a subject, and more particularly to a liquid injector for injecting a liquid, such as a contrast medium, into a subject who is to be imaged by an imaging diagnostic apparatus such as a CT (Computed Tomography) apparatus, an MRI (Magnetic Resonance Imaging) apparatus, a PET (Positron Emission Tomography) apparatus, or the like.
2. Description of the Related Art
Presently available imaging diagnostic apparatus for capturing fluoroscopic images of subjects include CT scanners, MRI apparatus, PET apparatus, ultrasonic diagnostic apparatus, CT angiography apparatus, MR angiography apparatus, and ultrasonograph. When such an imaging diagnostic apparatus is used to capture a fluoroscopic image of a subject, it is occasionally practiced to inject a liquid such as a contrast medium or a saline solution into the subject. There has been put to practical use a liquid injector for automatically injecting a liquid into a subject.
Such a liquid injector has a drive motor and a slider mechanism, and employs a liquid syringe that is removably mounted. The liquid syringe comprises a cylinder and a piston slidably inserted in the cylinder. The cylinder is filled with a liquid such as a contrast medium or a saline solution to be injected into the subject.
The liquid syringe is connected to the subject by an extension tube and set on an injection performing means. The injection performing means individually holds the piston and the cylinder and moves them relatively to each other for injecting a liquid, typically a contrast medium, from the liquid syringe into the subject.
The operator determines the rate at which the contrast medium is to be injected and the total quantity of the contrast medium to be injected, in view of various conditions, and then enters numerical data representing the rate and total quantity into the liquid injector. Based on the entered numerical data, the liquid injector injects the contrast medium into the subject at the rate and in the quantity represented by the entered numerical data. The injected contrast medium changes the image contrast of the subject, allowing the imaging diagnostic apparatus to capture a good fluoroscopic image of the subject.
Some liquid injectors are capable of injecting a saline solution as well as a contrast medium into the subject. For operating such a liquid injector, the operator enters, if desired, an instruction to inject the saline solution following the completion of the injection of the contrast medium, together with data representing the rate at which the saline solution is to be injected and the total quantity of the saline solution to be injected, into the liquid injector.
Based on the entered data, the liquid injector first injects the contrast medium and then automatically injects the saline solution after the contrast medium has been injected. The subsequently injected saline solution pushes the previously injected contrast medium, reducing the consumption of the contrast medium, and also reduces artifacts in the captured image.
Liquid injectors of the type described above have been devised and applied for patent by the applicant of the present application (see, for example, patent documents 1, 2 below).
Patent document 1: Japanese laid-open patent publication No. 2002-11096;
Patent document 2: Japanese laid-open patent publication No. 2002-102343.
The above liquid injector is capable of injecting a contrast medium into the subject in order to change the image contrast of the subject to a state which allows the imaging diagnostic apparatus to capture a good fluoroscopic image of the subject.
When a contrast medium for CT was actually injected into a subject by the liquid injector and a time-dependent change in the CT value, which represents the image contrast, was measured, it was found that even if the contrast medium was injected at a constant rate, the CT value was not constant, but rose nonlinearly and then fell, and remained at an optimum level for a very short period of time.
Therefore, the conventional liquid injector which injects a contrast medium at a constant rate that is represented by entered numerical data fails to provide optimum-imaging conditions in an imaging diagnostic apparatus combined therewith. For solving the above problem, it is necessary to change, with time, the rate at which the contrast medium is injected. For example, it is known in the art to divide one cycle of liquid injection into a plurality of phases and set numerical values of a liquid injection rate and a liquid injection time for each of the phases.
However, it is a complex procedure to set and enter numerical data for liquid injection rates which are actually to be changed with time. Even when the numerical values of the liquid injection rate and the liquid injection time represented by the entered numerical data are displayed in each of the phases, it is difficult to gain an intuitive understanding of time-dependent changes of the liquid injection rates.
Unskilled operators are unable to carry out such a complex procedure and may possibly enter inappropriate numerical data. In addition, the above process of setting numerical values of a liquid injection rate and a liquid injection time for each of the plural phases fails to set nonlinearly changing liquid injection rates.